Field of the Invention
The present invention relates to an optical fiber temperature distribution measurement device configured to measure a temperature distribution of an optical fiber along a longitudinal direction of the optical fiber, and a method of measuring an optical fiber temperature distribution.
Priority is claimed on Japanese Patent Application No. 2013-044272, filed Mar. 6, 2013, the content of which is incorporated herein by reference.
Description of Related Art
There have been widely carried out research and developments regarding distribution measurement devices configured to use optical fiber as sensors and to measure the distribution of a physical quantity of optical fiber, wherein the distribution is defined in the longitudinal direction of the optical fiber. One of the distribution measurement devices is an optical fiber temperature distribution measurement device which is configured to measure a temperature distribution along the longitudinal direction of the optical fiber by measuring Raman back scattering light (Stokes light and anti-Stokes light) generated in the optical fiber. The optical fiber temperature distribution measurement device is also referred to as R-OTDR (Raman Optical Time Domain Reflectometry).
Specifically, the optical fiber temperature distribution measurement device described above is configured to repeatedly supplying a pulse of laser via a side of the optical fiber into the optical fiber and sequentially receiving Raman back scattering lights from the side of the optical fiber, where the Raman back scattering light is sequentially generated by propagating the laser in the optical fiber. The temperature distribution along the longitudinal direction of the optical fiber is obtained by calculating the intensity ratio of the Stokes light and the anti-Stokes light at each measuring point along the longitudinal direction of the optical fiber (to be exact, by calculating the ratio of the average value of the intensity of the Stokes light and the average value of the intensity of the anti-Stokes light).
Recently, an optical fiber temperature distribution measurement device, which improves a dynamic range by inputting a train of light pulses into an optical fiber and performing a correlation processing (a demodulation) for a received light signal obtained by receiving Raman back scattering lights from the optical fiber, has been achieved. A code modulation using Golay code or Barker code is performed for the train of light pulses. Japanese Unexamined Patent Application, First Publication No. 2011-242141 discloses a conventional optical fiber temperature distribution measurement device which is configured to measure a temperature distribution by inputting a train of light pulses into an optical fiber, wherein a code modulation using Golay code is performed for the train of light pulses. Japanese Unexamined Patent Application, First Publication No. 2011-242142 discloses a conventional optical fiber temperature distribution measurement device which can prevent measurement errors due to the temperature variation of the device itself.
In some cases, an optical fiber temperature distribution measurement device configured to measure the temperature distribution by inputting a train of light pulses, for which a code modulation using Golay code, etc. is performed, into an optical fiber, does not accurately modulate the train of light pulses input into the optical fiber depending on a feature of an light source or a driving circuit (the driving circuit configured to drive the light source). If the optical fiber temperature distribution is measured using such a train of light pulses, the device causes a deviation (an error) of the measured temperature at a point where a temperature varies significantly (a temperature variation point) and/or a point where a loss varies significantly (a loss variation point). As a method of correcting such a deviation, a method of correcting the deviation using data obtained near the point where the device causes the deviation may be used.
An intensity of a received light signal obtained by receiving Stokes light and anti-Stokes light from an optical fiber varies depending on the temperature of the optical fiber. Therefore, in some cases, even if the method described above is used, the expected correction of the deviation is not achieved and the accuracy of measurement degrades instead. Since each of a light emitter (the light emitter includes the light source and the driving circuit described above) and a light receiver provided in the optical fiber temperature distribution measurement device has a temperature dependency, and the degree of the deviation described above varies depending on the environmental temperature of the optical fiber temperature distribution measurement device, it is necessary to correct the deviation appropriately in consideration of the environmental temperature in order to improve the accuracy of measurement.
According to one aspect of the present invention, an optical fiber temperature distribution measurement device which improves an accuracy of measurement by appropriately correcting a deviation of a measured temperature at a temperature variation point and/or a loss variation point, and a method of measuring an optical fiber temperature distribution are provided.